Hybrid metal packages, i.e., flat packs, have been used for many years to hermetically house hybrid and semiconductor discrete and integrated circuit chips. The basic flat pack comprises a square or rectangular frame having lead apertures formed therethrough and a bottom affixed to the frame. One or more chips are internally mounted to the bottom of the package and electrically connected to external circuitry by means of conductive leads or pins passing through the apertures in the frame. To ensure hermetic sealing and to preclude short circuiting between the leads and the frame, the leads are fitted within an insulative bead such as glass and the bead-lead combination is sealed in the apertures of the frame.
The traditional method of manufacturing frames for flat packs has required several tooling steps and multiple handling of the frame as it is being fabricated. The basic frame configuration is formed by coining or extrusion operations from metallic tubular stock. The coined or extruded frame is then subjected to a grinding operation to grind the frame to a predetermined height A deburring step is required subsequent to the grinding step to smooth the edges of the frame. One or more tooling steps are then required to punch the apertures in the sidewall members of the frame. Each of the four sides of the frame are punched independently, and if the aperture pattern in the various sidewall members is different, the aperture pattern for each side requires a separate set-up. The frame is then chemically processed and a bottom brazed thereto.
Lead frames for each frame sidewall are cut from strip stock and the individual conductive leads of each frame manually fitted with an insulative bead. The beaded lead frame is then disposed in combination with the corresponding frame sidewall by sliding the beads into corresponding apertures thereof. The frame assembly is mounted on specially designed carbon fixtures and fired in a furnace to seal the beaded leads within the apertures of the frame sidewall.
The above-described traditional method of forming frames for flat packs has several inherent disadvantages. Because the initial frame configuration is formed by coining or extrusion, the shape of the frame is limited to square, rectangular and/or circular configurations. Expensive, specialized tooling and lengthy lead times are required to produce flat packs having nontraditional sizes and shapes. A large inventory of tubular stock of various sizes must generally be maintained to ensure that proper stock is available. Moreover, the traditional methods of manufacturing frames requires numerous handling of the frames during the fabrication process which increases the overall expense of the finished frames and increases the possibility of damage to the frames during the fabrication process. In addition, flat pack frames formed by traditional methods limit the inside pin extensions of the conductive leads due to internal space restrictions and/or aperture sizing.